The black mamba (Dendroaspis polylepis), also called the common black mamba or black-mouthed mamba, is the longest venomous snake in Africa, averaging around 2.5 to 3.2 m (8.2 to 10 ft) in length, and sometimes growing to lengths of 4.45 m (14.6 ft). It is named for the black colour of the inside of the mouth rather than the colour of its scales which varies from dull yellowish-green to a gun-metal grey. It is also the fastest snake in the world, capable of moving at 4.32 to 5.4 metres per second (16–20 km/h, 10–12 mph). The black mamba has a reputation for being very aggressive, but it usually attempts to flee from humans like most snakes, unless it is threatened. Without rapid and vigorous antivenom therapy, a bite from a black mamba is almost always fatal.